Among substrates on which electronic components are to be mounted, a so-called cavity substrate having electrodes mounted on bottom surfaces of respective apertures (cavities) formed in an upper surface of a substrate body as well as electrodes mounted on the upper surface of the substrate body has hitherto been known. Since the cavity substrate enables three-dimensional arrangement of electronic components, the cavity substrate can make up a compact, high-density substrate.
In relation to such a cavity substrate, in order to print the electrodes mounted on the bottom surfaces of the respective cavities (i.e., cavity-area electrodes) and the electrodes mounted on the upper surface of the substrate body (i.e., flat-area electrodes) with paste, like solder, there has been used a screen print system built by coupling a first screen printer to a second screen printer. Specifically, the first screen printer subjects the substrate to screen printing by use of a mask having pattern holes that are provided on downwardly-projecting convex portions to be fitted to the respective cavities and that correspond to the respective cavity-area electrodes. The second screen printer subjects the substrate to screen printing by use of a mask having pattern holes corresponding to the respective flat-area electrodes.
Some of such screen print systems have hitherto been known to have cleaning units provided for the respective screen printers (see; for instance, Patent Document 1). After the substrate has finished undergoing screen printing, the cleaning unit is relatively actuated with respect to a mask in order to prepare for screen printing that is to be performed for a next substrate to be loaded. The cleaning unit brings a mask contact area, which is made by stretching a paper member over an upper end of the cleaning unit, into contact with a lower surface of the mask, to thus clean the paste adhering to the lower surface of the mask.